Final answer:
When a vessel slackens her speed, stops, or reverses her engines, it is to accomplish a change in motion, typically slowing down or stopping altogether.
Step-by-step explanation:
Under the rules, when a vessel slackens her speed, stops, or reverses her engines, it is to accomplish a change in motion. For example, if the ship is moving forward at a steady rate and then decelerates in the forward direction, it is slowing down. If the deceleration rate decreases, the ship continues to slow down but at a slower rate until it eventually stops moving.